The present invention relates to water-sensitive coloring sheets and more particularly to water-sensitive coloring sheets capable of forming colored images when water is applied thereto.
Known coloring sheets capable of forming colored images by application of water include those comprising a substrate, a colored layer formed from carbon black or the like on the substrate and a hiding layer formed from a white pigment of low refractive index or the like on the colored layer to hide the colored layer. With this type of sheet, the hiding layer portion wetted by the water applied becomes transparent and devoid of hiding power, making the colored layer visible therethrough, whereby colored images are formed.
This type of water-sensitive coloring sheet requires at least two applications of coatings in production to provide a colored layer of carbon black or the like formed on the substrate and a hiding layer formed from a white pigment to hide the colored layer, and involve the application of white pigment in an amount of about 15 to about 25 g/m.sup.2 for completely hiding the colored layer, presenting a cost problem.
Coloring sheets are also known which are capable of forming a color on a pH indicator-containing sheet by applying thereto a pH-controlled aqueous solution. This type of coloring sheets, however, can not develop a color if using only water.